Fix Iconv check in B2 in combination with ICU

Including ICU might bring another Iconv in (e.g. on FreeBSD)
which has different symbols.
So check for Iconv after adding the ICU options

build/Jamfile.v2

@@ -192,6 +192,13 @@ ICU_OPTS =
 exe has_icu : $(TOP)/build/has_icu_test.cpp : $(ICU_OPTS) ;
 explicit has_icu ;
 
+# Separate pair of obj & exe rules so the CPP file is built with the changed include paths
+obj has_iconv_with_icu_obj : $(TOP)/build/has_iconv.cpp : $(ICU_OPTS) ;
+exe has_iconv_with_icu : has_external_iconv_with_icu_obj : $(ICU_OPTS) ;
+explicit has_iconv_with_icu ;
+obj has_external_iconv_with_icu_obj : $(TOP)/build/has_iconv.cpp iconv : $(ICU_OPTS) ;
+exe has_external_iconv_with_icu : has_external_iconv_with_icu_obj iconv : $(ICU_OPTS) ;
+explicit has_external_iconv_with_icu ;
 
 # This function is called whenever the 'boost_locale' metatarget
 # below is generated and figures out what external components we have,
@@ -212,25 +219,8 @@ rule configure-full ( properties * : flags-only )
         }
     }
 
-    local found-iconv ;
-
-    if ! <boost.locale.iconv>off in $(properties)
-    {
-        # See if iconv is bundled with standard library.
-        if [ configure.builds has_iconv : $(properties) : "iconv (libc)" ]
-        {
-            found-iconv = true ;
-        } else if [ configure.builds has_external_iconv : $(properties) : "iconv (separate)" ]
-        {
-            found-iconv = true ;
-            result += <library>iconv ;
-        }
-    }
-    if $(found-iconv)
-    {
-        flags-result += <define>BOOST_LOCALE_WITH_ICONV=1 ;
-    }
-
+    local internal_iconv_target = has_iconv ;
+    local external_iconv_target = has_external_iconv ;
     local found-icu ;
 
     if ! <boost.locale.icu>off in $(properties)
@@ -256,9 +246,31 @@ rule configure-full ( properties * : flags-only )
             result += <source>icu/$(ICU_SOURCES).cpp
                       <library>/boost/thread//boost_thread
                       ;
+            # ICU might introduce an own iconv, so check for that.
+            internal_iconv_target = has_iconv_with_icu ;
+            external_iconv_target = has_external_iconv_with_icu ;
         }
     }
 
+    local found-iconv ;
+
+    if ! <boost.locale.iconv>off in $(properties)
+    {
+        # See if iconv is bundled with standard library.
+        if [ configure.builds $(internal_iconv_target) : $(properties) : "iconv (libc)" ]
+        {
+            found-iconv = true ;
+        } else if [ configure.builds $(external_iconv_target) : $(properties) : "iconv (separate)" ]
+        {
+            found-iconv = true ;
+            result += <library>iconv ;
+        }
+    }
+    if $(found-iconv)
+    {
+        flags-result += <define>BOOST_LOCALE_WITH_ICONV=1 ;
+    }
+
     if ! $(found-iconv) && ! $(found-icu) && ! <target-os>windows in $(properties) && ! <target-os>cygwin in $(properties)
     {
         ECHO "- Boost.Locale needs either iconv or ICU library to be built." ;